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Unformatted text preview: The Pennsylvania State University
Department of Civil and Environmental Engineering Lecture 10 Horizontal Alignment (Part 2) CE 321: Highway Engineering Fall 2007 Horizontal Sight Distance Horizontal Sight Distance Stopping Sight Distance Considerations for Horizontal Curves Source: Figure 3.14 from MKW Stopping Sight Distance for Horizontal Curves SSD = Rv s 180 s = 180 ( SSD ) Rv Rv = radius to vehicle's traveled path (radius to the middle of the innermost lane) s = the angle subtended by an arc equal to the SSD distance Stopping Sight Distance for Horizontal Curves
Ms = Rv 1  cos 90 (SSD) Rv Rv  Ms Rv SSD = cos1 90 Rv Rv = radius to vehicle's traveled path (radius to the middle of the innermost lane) SSD = stopping sight distance (ft) Ms = middle ordinate distance (ft) Source: www.answers.com Source: www.roadstothefuture.com Source: www.roadstothefuture.com Example Problem 1
Given a design speed = 60 mi/hr SSD = 570 ft Radius = 2300 ft at centerline Determine the minimum setback for an obstruction from the edge of the pavement Example 1 (con't) Radius at the Centerline of the Travel Lane
R = 2300  (12/2) = 2294 ft Example 1 (con't)
Solution: 90( SSD) M s = Rv 1  cos R v 90(570) = 17.68 ft M s = 22941  cos (2294) Clear from Edge of Pavement
17.68  6 = 11.68 ft Transition from Tangent Section to a Curved Section
Rotate the Pavement CrossSection Superelevation RunoffRunout Exhibit 337, AASHTO Green Book Transitions
Tangent Runout  length needed to accomplish change in outside lane cross slope from normal slope rate to zero. Superelevation Runoff  the length of roadway needed to accomplish a change in outside lane cross slope of zero to full superelevation. Spiral Curves Alternative transition method. Radius of the spiral at Tangent to Spiral (TS) is infinity. Radius of the spiral at Spiral to Curve (SC) is the radius of the curve (therefore the radius changes as the vehicle moves along the spiral). Spiral Description Spiral Curves The radius of a spiral, at any point, is inversely proportional to its length (constantly changing) The Degree of curve of the spiral increases at a uniform rate from zero at the T.S. to the Degree (D) of circular arc at the S.C. ...
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This note was uploaded on 04/11/2008 for the course C E 321 taught by Professor Pietrucha,martinkeller,michaelwi during the Spring '07 term at Pennsylvania State University, University Park.
 Spring '07
 PIETRUCHA,MARTINKELLER,MICHAELWI

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